John in NM
Wax rings are very useful for a lot of stuff, in addition to their intended purpose, so it didn't surprise me much to hear of this use. What surprised me is that someone would sell one at a yard sale!

There was an episode of Canada's Worst Handyman where there were a lot of toilet removal follies - one of which is that the intrepid amateurs mistook the wax for something else as they were removing porcelain shards from the drain.... That show was hilarious in many ways, potty humor aside.